High-gain amplifier tube



Dec. 12, 1950 R. ADLER ETAL HIGH-GAIN AMPLIFIER TUBE 4 Sheets-Sheet 1Filed May 3, 1945 a u u n n n n: pl

INVENTORSZ ROBERT A'DL'ER JOHN G, P RENTI'SS fifm g THEIR ATTORNEY Dec.12,1950 ADLER ETAL I 2,533,750

HIGH-GAIN AMPLIFIER TUBE Filed May 3, 1945 4 Sheets-Sheet 2 FIG. 4

INVENTOR'S .2

R OBERT A'DLER JOHNG. PRENTISS THEIR A TT RNEY' Dec. 12, 1950 ADLER ETAL2,533,750

HIGH-GAIN AMPLIFIER TUBE Filed May 3, 1945 4 Sheets-Sheet 5 F l G. 7

ubnnnnnnnnnn nnaaan Izunuu F l G. 9

8O 8! SEC ON D ANODE CURRENT E1 1 FIRsT ANODE CURRENT I! I D o l F I L JSECOND ANODE VOLTAGE PREFERRED OPERATING RANGE INVENTORS R0 8 E RT ADLERJ 0 HM G- P R NTI 55 THEIR A T ToR NEY Dec. 12, 1950 R. ADLER ETALHIGH-GAIN AMPLIFIER TUBE 4 Sheets-Sheet 4 Filed May 5, 1945 WIILFIJLNHHHHO HCIONV GNOOBS INVENTO RS I ROBERT ADLER JoHNGP RENTIS s B YCXTHEIR AT TORNEY Patented Dec. 12, 1950 HIGH-GAIN AMPLIFIER TUBE RobertAdler, Chicago, and John G. Prentiss,

Berwyn, 111., assignors to Zenith Radio Corporation, a corporation ofIllinois Original application May 27, 1944, Serial No.

537,704, now Patent No. 2,426,681, dated September 2, 1947.

Divided and this application May 3, 1945, Serial No. 591,712

6 Claims.

This invention relates to amplifiers, and more particularly to electrondischarge amplifier devices.

The present application is a division of our copending application,Serial Number 537,704, filed May 27, 1944, for High Gain Amplifier whichmatured into Patent No. 2,426,681 on September 2, 1947.

It is a fundamental object of this invention to provide an improved formof electron discharge amplifier device.

It has often been considered necessary to provide, in an electrondischarge amplifier device arranged to produce high gain, a cathodecapable of emitting large electron currents. It is, accordingly, afurther object of this invention to provide such an improved form ofelectron discharge amplifier device and circuit in which a cathodecapable of emitting only a small space current is provided. When such anelectron discharge amplifier device is arranged in accordance with thisinvention to produce high gain with the cathode emitting only a smallspace current, simultaneous savings are effected both in the powerrequired to heat the cathode and in the power dissipated in the otherelements of the discharge, device.

It is a corollary object of this invention to provide such an improvedform of electron discharge device in which only a small number ofelectrodes is utilized and in which the device is stable in operationand. rugged and capable of easy manufacture and assembly.

It is also an object of this invention to provide an improved form ofelectron discharge device in which, in a single discharge device, gainsin the order of at least 100 are readily obtainable.

The features of this invention which we believe to be novel are setforth with particularity in the appended claims. The invention itself,both as to its organization and manner of operation, together withfurther objects and advantages thereof' may best be understood byreference to the following description taken in connection with theaccompanying drawings in which:

Figure l is a sectional view in elevation of a preferred form ofelectron discharge device constructed in accordance with the invention;

- Figure 2 is a sectional view of the device illustrated in Figure 1,taken along the line 2-2 in Figure 1;

Figure 3 is a sectional view of an alternative form of the invention,taken as along the line 2'2 of Figure 1; a

Figure 4 is a sectional view in elevation of a 2 somewhat difierent formof electron discharge device constructed according to the invention;

Figure 5 is a sectional view of the device illustrated in Figure 4,taken along the line 55 of Figure 4;

Figure 6 is a sectional view of a modified form of electron dischargedevice similar to that illustrated in sectional elevation in Figure 4;

Figure 7 is still another alternative form of an electron dischargedevice constructed in accordance with the invention especiallyforoperation at low voltages;

Figure 8 is a sectional view of the device illustrated in Figure 7,taken along the line 8-8 of Figure '7;

Figure 9 is a graph illustrating certain characteristics of theinvention;

Figure 10 is a sectional view in elevation of still another embodimentof the invention;

Figure 11 is a sectional view of the device shown in Figure 10, takenalong the line llll of Figure 10; and

Figure 12 is a graph illustrating certain other characteristics of theinvention.

In Figure 1 an evacuated glass vessel [0 contains a filamentary cathodeII, a first control electrode l2, a first anode l3, a second controlelectrode 14 and a second anode IS.

The filamentary cathode II is fastened at its lower end to a support 16,mounted on a leadin wire I! which passes through the wall of the glassvessel 10, and is drawn tense through accurately dimensioned'holes inthe mica spacers l8 and I9 by a spring 20, to one end of which isfastened the supporting tab 2| on which the other end of the filamentarycathode II is fastened. The other end of the spring 20 is fastened tothe support post 22 which passes downwardly through the mica spacers I9and I8 respectively, and to the lower end of which is joined the lead-inconductor 23 which passes through the glass walls of the vessel l0.

A circuit is formed for heating the filamentary cathode I I from thelead-in conductor I! through the support IS, the cathode I I, thesupporting tab 2|, the spring 20, the supporting post 22, and thelead-in wire 23. r

The first control electrode structure is formed by winding a cylindricalconductor of suitable diameter around two supporting posts 24 and 25helically with the turns of the conductor spaced apart a suitabledistance. Each turn of the cylindrical conductor is fastened to thesupporting posts 24 and 25, as by welding or by providing slots in theposts 24 and 25 within which the cylindrical 3 conductor is wound, thematerial at each side of the slot being swaged over the cylindricalconductor. The assembled control electrode I2 is placed between the micaseparators I8 and I9 with the posts 24 and 25 extending through suitableholes in those separators and the filament II is thereafter passedthrough the holes in the separators I8 and I9 and tensed therein, theholes for the supporting posts 24 and 25 and the holes for the filamentII being suitably spaced so'that accurately determined distances aremaintained between the filament I I and the control electrode I2.

The first anode I3 and the second control electrode [4 are similarlyconstructed by the winding of a cylindrical conductoraround twosupporting posts, the diameter of the conductor and the spacing betweenadjacent turns on the supporting posts being in each case suitable toprovide a desired result, as will be explained more fully her'einafter.In each case" the supporting'{ posts i of" thefirst "anode I 3 andcontrol electrode i 2 are received within suitably positionedh'oles inthe n'iica separators'ifi and'lll so that accurate spacing is maintainedbetween'the control electrode -I 2', the first anode I3 and the 'se'condcontrol electrode-I4. It is notable .here that, with-thiscdhstiuctionand arrangement of a discharge 'device "and withcircuits described inthe above-hientionedparent case, it is not necessary-"to inaint'ain anyparticular alignment between the turns of the cylindrical conductor of'thefirst control electrode I2, the first anode I3, and-'the 'secondcontrol electrode It. :In other words, the vertical alignment of themeshes of those th'ree" electrodes may be leftentirely to chance.

Outside-of thesecond control electrode M the anode i5 isarrangedcylindrically between-the "rriica spacer's :I 8 and I29 withithezaxis o'f the cylinder coincident with athe :filarnent I I "Theanode E5 is supported by and electrically connected .to

its supporting"p'ost 30', which 'is placed symmetrically with thesupporting post 22, and the upper l endof' which supportsagetter-assernbly 3I'. filhe-sloiwer end of'the supporting post 30 isccnn'ected 'witha lead-in-conductor 32, whichextends through ithe'glas'scwallof the lenvelope I andprevidesfor "external electricalconnection to the anodeili; -Similar:lead-in conductors 34=and-z33fextend through thelglassvwall of the envelope ah"! "andareconnected respectively with supporting posts for thefirstanode I3 andthe second ccntrol electrode vI l, therehyproviding external electricalconnection respectively with those electrodes. A' fixedlead-.in'conductor-35 *passes through the glass wall of the envelope Illbetween-the-lead-in conductor I'I andthelead-in conductor '23, and isconnected with the suptportin'gpost 2 to .providean external electricalcconnection for the first control electrode I2.

In Fig. 2, the same numerals area-pplied to llike partsoi the dischargedevice. The central hole through the :mica'spacer l8 can be seen as atriangle with the'filarnent II! at one apex. The fiat; sided firstcontrol electrode l2 at its intermediate portions lies relatively-close.to the I Thess'econd .control electrode l ilalso ihas fiat sidessubstantially parallel with the fiat sides of 4 the first controlelectrode I2 and the first anode i3, and the flat sides of the secondcontrol electrode M lies substantially closer to the first anode it thanto the parts of the second anode I5 which receive the electron streamfrom the-cathode I i. That is, the shadowing .efiect iofzithe supportingposts as and 25 is such that the space discharge from the cathode IIpasses substantially perpendicularly through the fiat sides of thecontrol electrodes I2 and I4 and first anode I3 to impinge upon only aportion of the anode l5 facedby the fiat sides of the inner electrodes.

Purely "by .way of example, a typical set of dimensions for such anelectron discharge device is given to illustrate a specific manner inwhich the invention may be utilized. The filament II is made of tungstenwire a little more than ft inch in length and of such diameter that 50miliiamperes of current flowing through it produce a voltage drop acrossit of about of a volt, The helical wire with which 'the electrcdes 1:2},tS- and I4 are formed-is lllll2soflan inch in diameter. The firstcontrol electrode 52 is wound on the supporting posts in and .25 with-72 turns per inch,-and.is so wound that its fiat sidestare spaced apartby =0180f .an inch. Thatis, the

wcundavith lz turns per inch and its. flat sides' are spaced. apart'.200-Iof..an inch. The diameter of the cylindrical-anode ll-Brie .375.of'an inch, and the overall lengthiof sall of the elements between themica lspacerslIB-andaI 9 vis about T55 of-aninch.

Such dimensions provide that the distance between the second -c0ntro1electrode ..I l and the first anode-l3 is-rnuchdess than :the distancebetween the second-control electrode 14 and efiective parts of-the-anode I5. This spacing between-*the electrodes and the closemeshiof (the second control-electrode I4; which is wound with-72 zturnsper .-inch-,- provide that :the second control electrode l4 has arelatively high static amplificationvfactor with respect to the anode I5,

and that factor :may "be-made in the-orde-rcf .10

.or more. Such an electron discharge :device .made i accordance with theinvention, the usual ,precautions being taken as to upurityof materialsand-.ireedom fromcontamination within the envelope leiandawith care inevacuatingland gettering the device, may :be :us ed in circuits :asdescribed'hereinafter to produce great amplification, as great asseveral hundred times, while remaining stable in operation.Atthe'sameti-me, the discharge deviceis simple in constructionand ruggedand. is easy to manufacture.

a In general, the constructionof the secondcon- :trolelectrode I4 iscritical, ithe constructionof the remainder of the discharge :devicebeing quite similar to. that-of --a normalipentode. The'secondcontrolkelectrode 14 may; in a preferred form of the invention, --be;placed about twice as .farfrom the anode- I5 as from'the first anode L3and may have openings therethrough of such area that, when the secondcontrolelectrode is substantially at the potential of the cathode II,space current zpassing'through thatsecond'control electrode I4 isaifectedibythe electrode I4 inv such a way-that, when the potentials onthe anodes I5 and-"13am substantially. equa1',-=I= .the, 1 ratio betweencurrent the minimum ratio between those currents which is obtained whenthe potential of the second anode I is increased indefinitely in apositive direction. v

This condition does not obtain in a normal pentode in which a thirdelectrode is of relatively open mesh, the mesh being so wide that, withthe third electrode connected to the cathode, the third electrodeproduces substantially no efiect upon discharge current flowing from thesecond electrode to the anode. In other words, in a normal pentode,increase of anode potential, as is very -well known, does notsubstantially increase anode current. Expressed in another way, it isfrequently said that the internal anode resistance of a normal pentodeis extremely high, approaching infinity.

The construction of the second control electrode according to theinvention may be described in still another way. The spacing between thefirst and second anodes and the fineness 01 mesh are such that, when thesecond control electrode is operated at cathode potential, or moreaccurately at a potential near that potential at which electron currentbegins to flow into the second control electrode, and when there aresubstantially equal positive potentials on the anodes, current flowingin the second anode I5 is substantially less than the current whichwould flow infthe second anode [5 with substantially equal positiveanode potentials but with a more positive potential on the secondcontrol electrode l4. That is, the current in the second anode should beat least one-fifth less than the current which flows in the second anodeafter the second control electrode potential is made substantially morepositive, and it is preferred that the second anode current be in theorder of half the current which flows in the second anode after thesecond control electrode potential is made more positive. It is anotheraspect of this peculiar construction of the second control electrodethat it is capable of efiecting substantial changes in electron currentdistribution between the two anodes when its potential is changed insmall increments, its average potential being near cathode potential.That is, the static amplification factor of the second control electrodeis sufiiciently high that, when it is near cathode potential, it has asubstantial influence on the distribution of space current between thefirst and second anodes.

-As a general rule, the structures at the first and "second controlelectrodes will be somewhat similar insofar as their mesh and the sizeof the conductor from which theyare wound is concerned.

It should be noted at this point that, while it is 'preferredto have thesecond control electrode I4 closer to the first anode I3 than to thesecond anode 15, the second control electrode l4 can be constructed toproduce the requisite results without being so spaced. In thisconnection, it should be pointed out that the term closer must bedifferently interpreted when applied to different forms of controlelectrodes. Where the control electrode I4 is fiat sided as illustratedin Fig. 2, the term closer" should be given the natural meaning that theactual distance between the first anode l3 and the control electrode [4is less than the actual distance from the control electrode It to theanode [5, always remembering, of course, that thesedistances should bemeasured along a line perpendicular to the filamentary cathode II andperpendicular to the flat sides of the electrodes I3 and ll. 7

Where the electrode I4 is made generally cylin drical, the term closemust be given the meaning that the ratio of the diameter of the firstanode l3 to the diameter of the second control electrode 14 is greaterthan the ratio of the diameter of the second control electrode H to theanode l5.

In Fig. 3, there is illustrated a cross section of a second anode l5than to the first anode 13. While this is not' generally a preferredconstruction of the invention, it is possible to construct a device inthis manner and achieve resultsfalling within the scope of theinvention. Purely by way of example, certain dimensionsof the deviceillustrated in Fig. 3 are given to illustrate how the second controlelectrode 40 can be made so that it has a sufficiently large staticamplification factor to achieve the desired result. The filament H, theover-all length between the mica spac ers I8 and I9 of the elements, andthesize and spacing of the supporting posts may all be like those shownand described in connection with Fig. 1. Also, the spacing between thefiat sides of the first control electrode 12 may be .018 of an inch andthe spacing between the fiat sides of the first anode 13 may be .112 ofan inch. How

ever, the spacing between the sides of the second control electrode 40along a line perpendicu lar to the filament ll and perpendicular to thefiat sides of the first anode I3 is made .250 of an inch. and along thatsame line the diameter of the anode l 5 is made .320 of an inch.

Such an arrangement as illustrated in Fig. 3 has in the second controlelectrode 40 a smaller static amplification factor -than if theelectrode 40 were closer to the first anode [3 than to the second anodel 5, but the second control electrode 40, having 72 turns per inch ofcylindrical conductor .002 of an inch in diameter, is, when near cathodepotential, capable of substantially influencing the current distributionbetween the anodes l3 and I5.

In Fig. 4, there is illustrated an electron discharge device which isespecially constructed for operation at substantially lower electrodepotentials than the device illustrated in Fig. 1. Many elements aresimilar to the elements illustrated in the device of Fig. l and aregiven like reference characters. The first control electrode 50, thefirst anode 5|, second control electrode 52, and the second anode 53 areall constructed with different dimensions from the corresponding eleo--trodes of Fig. 1 for the purpose of providing lower potential operation.The first control electrode 50 is made of somewhat more open mesh sothat a relatively low positive potential on the first anode 5| isefifective to draw a substantial electron current flow from the cathodell through the first control electrode 50. Similarly, the second controlelectrode 52 is made with somewhat more opeirmesh so that the anode 53can draw asub The second control electrode 40 is ace-ates *1? tween thecontrol electrode 52"and the first anode By sway-u of teXa'mpletoillustrate .one manner in which the device of Figa maythe-constructed,

theiirst controlcelectrodeiu may,be :woundwith. 6=l turns per inchtofcylindricalconductor .002ofl aminch in diameter,. wound.helicallyaround, the 1 supporting posts 24 and 25. The first; anode/i" maybewound with the same size conductor, but" withl 50 -lturnsperinchpanduthe second control.v electrode 52amay be .wound with the-samesize conductorbut with 64 turns per inch In-iFig." 5,.like- .parts aregiven the same -refer encanumerals and the shapes of the electrodes 50;.5I 52-and 53 may,be.seen somewhat more clearly. The controlelectrodes50 and 52 and the first anodefii are woundwith flat sides, like thecor-responding electrodes shown in Fig.2, and the anode53 iscylindrical. The spacing between-the opposite fiat sides of the firstcontrol electrode '50 is .018 of aninch, and the spacing between theoppositeafiat sides of the-first .ancdefil and the second controlelectrode 52 are respectively .086. of -an inch and 136 of an inch. Thediameter of the anode 5 3 is'.250 of aninch.

With the second control electrode52 substantiallycloser. tothe=firstlanode 5i than to the second anode 53,land withthefirst-an'odefil relatively-closer .to the first control electrode 56,the two control.electrodesubeingof more open mesh, the anodes .51 and 53may be operated at lower potentialsfthan is the. case withithe deviceillustrated in Fig.1; For .example anode supply potential for the.device. of Figs; 4 and 5 may be in the. order-f and volts Even ,withsuch cannot: be made indefinitelylow; Contact potentials, whichare in.theorder of one volt, and which are duevtosurface conditions of thevarious electrodes, the surface conditions being frequently alteredbycontamination with cathode coating materiahmay affect very undesirablythe anode currents. -Such contact potentials vary markedly v'fronronedischarge device to another and 'Eurthermore they vary during use of thedischarge ,cevicei- These contact potentials affectthe-actual:potentialof every electrode in the dis-v charge tdeviceandrparticularly affect the effective bias potential of thesecondcontrolelectrode. If the staticlamplification factor of the secondcontrol electrode. is high, the supply potential for both anodes-must be:high compared t-O-'-th8 COll taCt; potential of the second controlelectrode multiplied by its static vamplification factor If the supplypotential for the anodes is not-high. compared to the contact potentialofv the; second controlelectrodeltimes its static ampliflcation factor;the contact potential may affectlthe anodecurrent adversely, and mightevencut off completely the current flowing in the 1 second anode. In anycase, in the particular circuits-with which this discharge device isparticularly adapted to be used,itis undesirable that thecontactvpotential of the second control electrodes afifect the currentin either anode to any large, extent.v [I I Bearing in mind the effectofccontactpotential otsthesecond control-electrode, whereflthoseconafled second anode. Like:-reerence numerals area seconds controlelectrode 4 are-the samer beingrt s tact-potentialsare the order ofaonavoltn tastthe-y usually. are) it isevident :thatvif itbedesired'i tooperate-the anodes from supply potentialsli the order of-twenty ,volts,the static amplification a factor of the secondcontrol electrode shouldnot-i exceed a factor in the order of 10.- Anode supplies: potentialslower thaniabout 15 volts cannot Safely be used, .unless--contactpotential is reducedlcors respondingly lower .thanll :voltja In-lFig6,,there isillustrated linacross sectional taken: perpendicular to Ithecfilamentary rcathodek a discharge-device similan toflthatillustrated in Figs. .1' and-2, .particularlyy-im thatithe s econd lcontrol electrode -is mounted -;c1oser. ..to "the l-f rst J anodethanltothe second anode but with a .modi J applied to similar parts.- Difieientmica-spacers u areprovided, of whichthe lowernne 60-is-il1us.---, I,trated, in order to support the filamentary -.cathode. I I andthe-:first -control-l electrtxzletfl,- first -anode I3, andsecondsanode:I4 oifscenten-withm respect-to the glass-envelope. I 0. Ananode-.6 I l of relatively4small:.areacompared-to one of-.-t he-: flatsides of I the second icontrolaelectroda I 4, iss

supported on a supporting ,post 6 2 .-.-between-the :1: 'mica separatorsand -isplaced substantially.syml-t metrically gwithrespect to a planepassing throughfa the filament .i I perpendicularly to the flat -sidez-I of the-second controllelectrodetfl. f p I Byiway of illustration,..the dimensions for-ca.

as .follows. The. spacingsbetweenthe .flat sides;- of the controlelectrode I2-are=the same,beings v .018 ofaninch, andsimilarlyithe-spacingsbetween the fiat sides of the .first anode -V;I 3andfiof th respectively ,-.1l2 of-an'inch and -.200 ofe-anrinohtge The 3distance- -from-the filamentary cathode. I to the smallanode--.6I-is.-.18'7: of an-linchs; As the case with thedeviceilliistr-ated m Fig.1; @the vi mesh \of-theelectrodes; I2,- I 3andal 4 is-:respectiv ely 72 turns per inch, turns per inch,rand 72turnsper 7 inch. 7 V v Bymaking. the area'of the-anode- 6 I small,and inwfact substantially smaller: than n-the' -effective area-of the secondcontrol-electrode1.4,:the inter nal: anode resistance of the anode BIis-made hig' andthe effect of-potential-changes on the 'secon controlelectrode I t :upon the flow of: current toa th first anode i3 issubstantiallyfreduced-i Thi structure -of.an.electronrdischarge deviceis espe' cially' useful in' a specia31-:-circuit employingregen erationsThat is; in a circuitdnwhichpotentials1 changes appearing" on thefirsttanode': Iii-(whens;

signal? potentials-are limpressedaon the first control. electrode 1 2 )1are impressed upon the-seconds;

,of the-second control electrode I4 Supon current fiowingiothe-firstanode.- l 3 isereducedcnso'tha controlaelectrode I 4-, thedischarge-device acts notonlye-lika a cascadedpairottriode amplifier-ast but also acts regeneratively. The regenerativee effect,ofspotentialsaimpressed on-secend'control electrode; I 4 day-the firstanode I 3, up on 'thespace a? current flowing Ito the-first anode I3-'may=lbe:"so'- great, as to .causell self-induced.-=oscillation. Bymakingtheeareaiof. the-anode 5| small, ;theeffects.

9 trode I4, the change in current distribution between the anodes I3 and6| caused by the resulting efiect of the second control electrode I4 isin aiding relation on the first anode I3 and is therefore regenerative.This is true because an increase in the total cathode current from thefilament II, caused by a change in potential in the first controlelectrode I2, causes a reduction in the positive potential of the firstanode I3 and, when such reduction in potential is impressed on thesecond control electrode I4, causes a still further reduction in thepotential of the first anode I3 by reason of the still further increasedcurrent flowing into the anode I3 because of the change in currentdistribution between the anodes I3 and BI induced by the change inpotential on control electrode I4. This change in current distributionbetween the anode I3 and BI is suflicient to cause the potential ofanode -6I to rise instead of falling as it would if the potential ofsecond control electrode I4 had not changed. Because the anode BI issmall, the first anode I3 takes substantially all of the electroncurrent from the cathode II over most of its area and the controlelectrode I4 is therefore not effective to change the anode currentdistribution between anodes I3 and 6| as much as if the anode 6Ientirely surrounded the control electrode I4. Consequently, theregenerative effect of potential changes of second control electrode I4upon the first anode I3 may be made sufficiently small that self-inducedoscillations cannot be started. Stable operation is therefore possible.

In Figure '7 there is illustrated an alternative form of electrondischarge device which is especially suitable for operation with lowanode supply potential, and without any sacrifice in gain by increase inmesh size of control electrode as in the case of the device illustratedin Figures 4 and 5. In this figure many elements are similar to thoseillustrated in Figure 1 and are given like reference character. A spacecharge electrode 10 is provided adjacent to the filamentary cathode II,and is followed consecutively by a first control electrode I I, a firstanode 12, a second control electrode I3, and a second anode I4. Theseelectrodes are all held in proper spaced relation by suitable micaspacers I and IS. The space charge electrode I0 is provided with anexternal connection through a lead-inconductor 19 extending through theglass wall of the envelope Ill.

The space charge electrode i0 is constructed so that it may be operatedat a small positive potential, with the result that a substantialcathode current is caused to flow through the first control electrode Hto the first anode I2, even though the first anode I2 is operated with aVery small anode supply potential (for example, as low as fifteenvolts), and even though the static amplification factor of the firstcontrol electrode II with respect to the first anode 12 is substantial.In such a device, as in the ones previously described, the staticamplification factor of the second control electrode l3 may be made highwith respect to the anode 14, even though the anode supply potential forthe anode 14 is very low, for example, as low as fifteen volts.

As a specific example, to illustrate exactly how one device of the typeillustrated in Fig. 7 may be constructed, the space charge electrode itmay be wound with 64 turns per inch of cylindrical wire of two thousandsinch diameter, the first control electrode ll with 80 turns per inch,the

first anode 12 with 50 turns per inch, and the second control electrodeI3 with 72 turns per,

inch, all being wound with cylindrical wire of two thousandths of aninch diameter.

Fig. 8, being a sectional view along the line 8- S of Fig. 7, makes itevident that the first con trol electrode ll is closer to the cathode IIand to the space charge electrode '50 than it is to the first anode l2,and similarly the second control electrode 53 is closer to the firstanode "52 than it is to the second anode 74. As a specific example, thediameter of the electrode shown in Fig. 8, wound like those describedspecifically in connection with Fig. '7, such diameters being takenalong a line perpendicular to the filamentary cathode l I and to theflat side of the second control electrode 13, may be respectively 0.018inch, 0.0%? inch, 0.125 inch, 0.2 inch, and 0.375 inch.

Such an arrangement as shown in Figs. 7 and 8, in which a space chargeelectrode I0 is provided is especially useful in connection withapparatus such as a hearing aid in which it is highly desirable, notonly that low potential be necessary for all of the electrodes, in orderthat very small wearable batteries may be utilizedtc supply thepotentials, but also that the current and power drain required by thedischarge device be extremely small, so that the small Wearablebatteries may have a reasonably long life.

In Fig. 9 certain operating characteristics of all the discharge devicesso far described are illustrated, anode currents being plotted asordinates, against second anode voltages, as abscissae. Thecharacteristics illustrated are present in these discharge devices,provided cathode temperatur'eis high enough that electron emission fromthe cathode is not temperature limited. When the second anode voltage isverylow, and with a fixed first anode potential high enough to cause asubstantial first anode current to flow with a zero potential on thesecond anode, with a small negative bias potential with respect to thecathode on the first control electrode, and with the second controlelectrode maintained at cathode potential, or more accurately at thatpotential at which the second control electrode just begins to takeelectron current, all current flows to the first anode. Curveillustrates the variation in first anode current under those conditionsas the second anode voltage is increased from zero volts with respect tothe cathode to a high positive voltage, and curve BI illustrates thevariation in the current flowing in the second anode as the second anodevoltage is so changed.

Curve 8!] shows that the first anode current is of substantial amountwhen the second anode voltage is zero with respect to the cathode andremains substantially constant as the second anode voltage is increasedto a substantial ositive voltage with respect to the cathode. At somesubstantial positive second anode voltage, for example, a voltage in theorder of ten volts, the first anode current begins to decrease as thesecond anode voltage increases, and continues decreasing, finallyapproaching a limiting minimum current which does not decrease as thesecond anode voltage approaches infinity.

Curve 8| illustrates that the second anode current is zero when thesecond anode voltage is zero with respect to the cathode, and remainszero as thesecond anode voltage is increased in that second anodevoltage at which the anode currents are equal and that second anodevoltage at which the second anode current first appears that it ispreferred to operate the discharge detenn s-stain -twt steamin pasts tsvice made according to this invention. With the second control electrodeconstructed in accord-"' ance with the invention, the anode currents andthe anode voltages'within this preferred operat- "ing rangeare of normaland reasonable magnitude, and the dircharge device may be used withvarious circuits to produce extremely high gain" amplification. With thesecond control electrode so constructedaccording to the invention, thes'econdanode voltage is impractically high, and too high for practicaloperation of the discharge device, where the second anode current isnear maximum and the first anode current near minimum. It is in thatregion that the normal pentode operates, and it is able to operate inthat region with a smaller anode voltage by reason of a differentconstruction of its third grid, cominonly called the suppressor. Thesuppressor "electrode in a normal 'pentode is made with an open mesh sothat it does not substantiall affect 'vviththedevic'es "illustrated inFigures'l through 1 8, that is, the discharge device illustrated 'inFigure isconstructed so that the anode supply potential for the anodes92 and 94 may be in the order of 200 volts, and shouldbe in the order ofat least 45 volts. The first control electrode 9-3, between the firstanode 92 and thecathode 9!, and the second "control electrode 95betweenthe first 'aLn'o'deBZ and the secondanode 9's,are-100th Inade to have'arelatively high static amplification factor. The second'c'ontrolelectrode 195 -may;

forejxample, be'so constructed that its static'arnfplification factor isin the order-of or more, thereby necessitating that the supply"potential for the second anode 94 be large relative to the staticamplification factor of the control electrode 95 multiplied by thecontact potential, which is in the order of 1 volt.

Except lfor the construction of the five electrodes of the dischargedeviceiin Figure "10 so that the anodes "operate at higher positive 130-ftentials, lands?) that thet'cohtlol' electrode 95 hasi a' higherstatic'amplification"factor, the genjeral-prin cipl'es of"the-construction and operao f this discharge device are much the sameas those illustrated in Figures '1 through *8.

Purelyb'y way of example, specific dimensions ferjtl ieelectrodes'aregiven. Thedia'riieter of ith e cylindrical unipote'ntial indirectlyheated :cathode 9 l is ODfl'T-inCh. The firstcontrolelectrode-'9?menses-cf was OEGOSiI'icE in diam ter,

9 2 is formed 0f" ii/ire whose diameter-"1's 0.003 inch won aspiranyarounatwt supporting pests as and 99 'with aims per inch. Thesccndcolftrol eletrode fi is 'foimd of Wire Wlidsiii- 'anieteris 0.002 inchwound spirally around two s porting posts 100 and 101 with 72 turns perinch. These'cond anode 94 is formed of sheet meta-l havin fiat wingportion -'on opposite sidestithe heated fcatho'de 9 I.

V In Figure 11 fa 'se'c tional View of the device shown inFigu're 1'0taken along the line ll-= illustrate "more-de rl the general shapeoff-the various electrodes of the device in a plane p'e'rpendicular tothe axis of the cathode '91. [The Wings 102 and H13 oi" the anode 94 lieparallel'to eachoth'e'r and are spaced ar'oartlkSOO inch. The wings I02and IE3 lie in planes which are p rallel with the axis of the indirectlyheated cathode 91. The second control electrode 95 hasflat side's whichare generally parallel with the wings "Ill? and "13 of the anode 94, andthe'fla't sides of the second control electrode 95 are spaced "apart by0.270 inch; Similarly, the first anode 92"has flat opposite sidesgenerally parallel'with the Wings H12 and 103 of the anode 94, 'and 'the"fiat opposite sides are spaced apart by "0.172

I inch. The distances by which these flat sides are spaced apart are allmeasured along "a line perpendicular to the axis of the cathode 9! and"to the planes I02 and I03 of the anodej'lll. Along that same line theopposite curved" sides "of the first "control "electrode 93 are spaced"apart by 05075 inch. It should be noted that "theo'ppos'ite "sidesoithe first control'electrode 93 are 'notfl'attenedjbut are-rounded, sothat the control electrode 93 is substantially equidistant froinfallemitting'parts of the cathode 9|. The shadowing effect "of the controlelectrode 'sup- Sporting post 96 and 91 is eifectiv'e to-suppress"electron'emis'sion from "portions of the surface "(if the cathode 9|near a plane passing through thefsupp'ortinglpos'ts 9B and 91. v

'Th'eelectrodes 9| through 95 "are all supfported'insymmetrical'relation with each other between mica spacers lll l and I05,which in turn are held iniprope'r relation to one "another and which'arejheld a art in fixed relation-by iposts I08 a"nd"l'09; A suitablegetter assembly I l-'0 -is supported in any desired fashion in the upperportion of the envelope 90.

Individual external connections 'for the five electrodes 9| through areprovided, each extending through the glass 'wall of the envelope 90. Alead-in conductor Ill provides an external'connection for "theunipotential cathode 9|. A lead-in conductor I [2 provides an externalconnection for the first control electrode 93. Lead-in connections H3,H4 and H5 respec-- tively, provide external connections for the firstanode 92, second control electrode 95, and sec 'ond anode 94.Lead-inconductors ll6..provide external connections -through whichsuitable continuous or alternating current may be suppliedto"a"re'sistance heater \vithi'n tlie unipotential cathode 9|,

In Figure 12 certain characteristics or a discharge device constructedinacc'o'rdanc'e with this invention are presen'ted'ih a somewhatdifferentlight than in Figure 9.]In Figure 12"the currents flowing inthe second anodeareplotted as ordinates 'andthe potentials ofth'e's'e'cond anode-amended abscissae: Curve I20 is similar insignificance to curve 8| of Figure 9 being taken with a fixed positivepotential on the first anode, with a small negative bias potential onthe first control electrode, and with no bias potential on the secondcontrol electrode. That is, curve I is taken with the second controlelectrode connected to the cathode, or more accurately adjusted to thatpotential at which current just begins to fiow in it.

Curve l2| may be observed under similar conditions, but with thepotential of the second control electrode made a little more negativethan is the case with curve I20. The curves i1- lustrate that the secondanode current is throughout the operating range, with. a substantialnegative bias potential on the second control electrode, substantiallyless than with no bias potential on the second control electrode.

-By referring to points on the curves I20 and |2| on a perpendicularline, such as the line (22, it may be determined how much current change(delta I) can be expected in the second anode in response to apredetermined small voltage change of the second control electrode, thefirst and second anode voltages remaining constant. Of course, in actualuse, application of a small negative bias potential to the secondcontrol electrode tends to decrease the second anode current with acorresponding increase in the second anode voltage, because the secondanode must be connected to a source of supply potential through a loadimpedance. Consequently, when a load impedance is connected with thesecond anode, the actual change, or reduction, in said second anodecurrent upon an increase in negative bias potential of the secondcontrol electrode is smaller than might otherwise be expected. Expressedanother way, the static transconductance from the second controlelectrode to the second anode is always greater than thetransconductance between those two electrodes measured with a. loadimpedance connected with the second anode.

As pointed out previously, the peculiar construction of the secondcontrol electrode makes it possible to have these controlcharacteristics with the second control electrode in the region ofcathode potential. The normal pentode with a suppressor electrodeoperates at second anode voltages above the operating range indicated inFigure 12, and a suppressor electrode has a negligible transconductanceover a substantial range of voltage near the cathode voltage. As amatter of fact, the second anode current does not drop to zero until thesecond anode voltage has reached P zero voltage with respect to thecathode, unlike the characteristic of the prefered form of dischargedevice according to the invention in which the construction of thesecond control electrode keeps the second anode current at zero evenwhile the second anode voltage is at substantial positive level.

While we have shown and described the particular embodiments of thisinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing fromthis invention inits broader aspects, and we, therefore, aim in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of this invention.

We claim:

1. An electron discharge device having a plurality of electrodesincluding a source of electrons, a first control electrode consisting ofa mesh having openings of a first size, a first anode consisting of amesh having openings of a secondsize, greater than said first size, asecond control electrode consisting of a mesh having openings of'a thirdsize less than said second size, and alsecond anode, said electrodesbeing mounted serially and consecutively adjacent each other along theelectron stream between said source and said second anode, said secondcontrol electrodebeing closer to said first anode than to said secondanode whereby said second anode is operative at a low positive potentialwith respect to said source.

2. An electron discharge device having a plurality of electrodesincluding a source of electrons, a first control electrode consisting ofa mesh having openings of a first size, a first anode consisting of amesh having openings of a second size greater than said first size, asecond control electrode consisting of a mesh having openings of a thirdsize less than said first size, and a second anode, said electrodesbeing mounted serially and consecutively adjacent each other along theelectron stream between said source and said second anode, said secondanode having an area lying in said electron stream which is smallcompared to that area of said second control electrode lying in saidstream, whereby stable operation of said electron discharge device isassured.

3. An electron discharge device comprising a plurality of electrodesconsecutively adjacent each other along an electron stream including: asource of electrons; a first control electrode of a mesh having openingsof a first size; a first anode of a mesh having openings of a secondsize greater than said first size and positioned at a distance from saidfirst control electrode greater than the distance from said firstcontrol electrode to said source of electrons; a second controlelectrode of a mesh having openings of a size substantially equal tosaid first size; and a second anode positioned at a distance from saidsecond control electrode greater than the distance from said first anodeto said second control electrode.

4. An electron discharge device comprising a plurality of electrodesconsecutively adjacent each other along an electron stream including: asource of electrons; a first control electrode of a mesh formed by awire wound helically at a first winding pitch and positioned at a firstdistance from said source of electrons: a first anode of a mesh formedby a wire wound helically at a second winding pitch greater than saidfirst pitch and positioned at a second distance from said source ofelectrons substantially equal to six times said first distance; a secondcontrol electrode of a mesh formed by a wire Wound helically at awinding pitch substantially equal to said first pitch and positioned ata third distance from said source of electrons substantially equal toten times said first distance; and a second anode positioned at adistance from said second control electrode substantially equal to twotimes the distance from said first anode to said second controlelectrode.

5. An electron discharge device comprising a plurality of electrodesconsecutively adjacent each other along an electron stream including: asource of electrons; a first control electrode of a mesh formed by awire wound helically at a pitch in the order of '72 turns per inch andpositioned at a distance in the order of .009 of an inch from saidsource of electrons; a first anode of a mesh formed by a wire woundhelically at a pitch in the order of turns per inch and positioned at adistance in the order of .056 of an inch from said ipit chin the orderof '72tiirns per inch and pos'iti n'data distance in'the order of.100'of an inch f'roinsaidsoi'irce of electrons ;''and asecond anode*bositlioned at a distance in the order of .187 of an infh fromsaid"source of electrons.

6. electron'discha'r'ge device having a plu- '-'rality' of electrodesincluding a source of elec- "ti'onsafirs't control electrode'eonsistingof amesh having openings of a fi'rst'size, a first anode consisting of amesh having openings of a "second sizegraterthan-said first size,'asecond control electrode consisting of a mesh 'havingop'eningssubstantially equal to saidfir'st size, and a second anodasaidelectrodes being mou'nt'ed'serially and consecutively adjacent "eachother along the electron stream flowing between said source and said*second anode, 'said *secondcontrol electrodelying closer to said firstanode than to said second anode; Whereby'said second anode is operativeat a --low"=positive potential with respect to said source, said secondanode havingan area lying in said electron-stream which is smallcompared to ifiliatarafdfafd 5e u said elegtrdn streak-1 ix/Herebyself-induced os l1- latibn or 'sai'd 'elctrondis'liafge device is iii-e-RD a JOHN G. 'PR TISS.

The following references areof record in'the file of this patent; V

UNITED S ATES-PATENTS 5511" Overbeck' 11113 3051946

